If I had a dollar for every time someone on FR said "sanctions don't work", I could buy a whole lot of flour!!!
The problem with sanctions is not that they do not work—it is that they are a form of warfare.
If you start sanctioning too many countries (especially powerful ones) they may decide to band together and declare war on you.
Example: The sanctions on Japan are generally agreed to be one of the key factors that caused them to attack Pearl Harbor.